In electrical equipment having multiple modules or units that are interconnected, it is desirable to provide a keying system that uniquely defines plug and receptacle pairs that are to be mated. There are many such systems in use in the industry. For example, U.S. Pat. No. 4,778,411 discloses mating electrical connector housings having hexagonal nests formed therein containing hexagonal shaped keys that are positionable in any of six unique angular positions. Each housing has a key that is in axial alignment with a corresponding key in the other housing. Mating of the two housings is prevented unless the two keys are in mutually complimentary angular positions. The shanks of the keys include an undercut that mates with an inwardly facing bead on the interior of the nest and a split end to provide a snap action when the keys are pressed into their seats.
U.S. Pat. No. 5,370,557 discloses a keying arrangement for low profile electrical connectors. The opposing ends of a mating plug and receptacle have polygonal openings formed completely through their housings that contain opposing polygonal-shaped keys that are axially aligned. Each of the keys is retained in its respective polygonal opening by a pair of wing-like flanges extending from the key that overlies a first surface formed in the housing adjacent the polygonal opening and a locking tab projecting from the key that underlies another surface spaced from the first surface.
Additional keying arrangements are needed which are novel in design and structure over prior art keying arrangements. In particular, what is needed is a connector keying arrangement having a novel design and structure that effectively prevents inadvertent mating of the contacts of a first connector with the contacts of a second connector in an electrical connector assembly when the electrical ratings of the first and second connectors are different. What is also needed is a connector locking arrangement having a novel design and structure that effectively connects and interlocks the two connectors of the electrical connector assembly.